Ellicottville Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Ellicottville Observatory clear sky chart from 2005-11-06 to 2025-01-22.

This page is a summary of past forecasts. Even though it's based only on forecasts, some people use these pages as clue to a site's climate. But climate data based on actual observation should be preferred (if you can find it!).

Cloud, Transparency and Seeing forecasts are summarized individually. But because good observing conditions require a combination of minimum cloud cover, transparency and seeing, the individual forecast summaries can be difficult to interpret. The observing conditions section counts the combinations of conditions needed for common types of astronomical observation.

Observing Conditions

The following tables count the occurrence of the combinations of forecast and darkness conditions needed for different observations. Conditions are rated by by what percentage of the hours the observation would likely be attempted are usable.

Observation Type	Minimum conditions for hour to be usable				Out of hours
	Clear of Clouds	Transparency	Seeing	Sky Brightness
Planetary:	50%	(no limit)	Average	(no limit)	Nighttime Hours
Deep Sky:	70%	Average	(no limit)	5.9	Nighttime Hours
CCD Imaging:	70%	Below Average	Poor	(no limit)	Nighttime Hours

Percentages are of nighttime hours per month, or per year, when a particular observing conditions was met. Deep Sky percentages never exceed 50% because the moon is up half the time. Deep sky percentages are much lower for charts at high latitudes because of fewer dark hours in the summer.

Overall

By Month

Individual Forecasts

The length of each colored bar in the "occurrence of each Forecast" column is proportional to the number of times the chart forecast that color. The percentages are of the total number of hours per month, or per year, with a particular forecast. The colors as the same as those used in clear sky charts.

Note: Transparency probabilities are only counted for those hours that have 30% or less cloud cover. Seeing probabilities are only counted for those hours that have 80% or less cloud cover. If that's too tricky, try Observing Conditions instead.

Overall

		Occurrence of each Forecast	Data Points
Cloud Cover	Day	16% 14% 5% 10% 5% 4 4 3 5% 6% 27%	105153
	Night	16% 16% 6% 11% 6% 4 4 3 4 5% 25%	104204
Transparency	Day	56% 5% 11% 18% 9% 1	108759
	Night	59% 5% 10% 17% 8% 1	108687
Seeing	Day	26% 18% 28% 17% 9% 3	14773
	Night	25% 17% 26% 22% 9% 1	24319

By Month

Percentage Cloud Cover NE (2006-)
Color Meanings: Overcast 90% covered 80% covered 70% covered 60% covered 50% covered 40% covered 30% covered 20% covered 10% covered Clear
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	13% 25% 14% 17% 7% 3 3 2 2 4 11%	2597
	11th to 20th	Day	11% 22% 10% 22% 7% 4 2 2 2 3 13%	2879
	21st to end	Day	21% 19% 9% 19% 8% 5% 4 3 3 3 7%	3133
February	1st to 10th	Day	15% 22% 7% 17% 9% 5% 4 2 3 3 14%	1710
	11th to 20th	Day	13% 17% 8% 19% 8% 4 4 3 4 3 15%	1663
	21st to end	Day	18% 17% 6% 13% 7% 4 3 3 4 5% 19%	1500
March	1st to 10th	Day	18% 15% 8% 10% 4 3 3 3 4 5% 27%	3432
	11th to 20th	Day	10% 23% 8% 10% 4 3 4 3 4 6% 26%	3480
	21st to end	Day	18% 14% 6% 13% 5% 4 4 3 4 5% 25%	3815
April	1st to 10th	Day	16% 18% 5% 8% 5% 4 4 3 4 6% 27%	2267
	11th to 20th	Day	19% 15% 3 6% 3 3 4 4 5% 6% 32%	2254
	21st to end	Day	21% 13% 3 8% 5% 3 4 3 4 5% 31%	2454
May	1st to 10th	Day	23% 11% 3 7% 4 4 4 3 5% 6% 30%	4108
	11th to 20th	Day	18% 11% 3 9% 5% 5% 6% 4 6% 7% 26%	4356
	21st to end	Day	13% 7% 2 6% 5% 5% 5% 4 6% 8% 40%	4837
June	1st to 10th	Day	18% 9% 2 7% 5% 4 4 4 6% 8% 34%	2660
	11th to 20th	Day	16% 8% 2 7% 5% 4 5% 5% 6% 8% 33%	2660
	21st to end	Day	17% 6% 2 6% 4 5% 6% 4 6% 8% 35%	2660
July	1st to 10th	Day	11% 6% 2 7% 5% 5% 6% 5% 8% 9% 35%	4440
	11th to 20th	Day	13% 7% 2 6% 5% 5% 5% 5% 8% 10% 35%	4440
	21st to end	Day	9% 7% 3 8% 6% 5% 6% 5% 7% 8% 36%	4466
August	1st to 10th	Day	17% 8% 3 7% 4 5% 5% 4 7% 8% 32%	4104
	11th to 20th	Day	15% 8% 3 9% 7% 6% 7% 5% 7% 8% 25%	4044
	21st to end	Day	14% 7% 2 6% 4 5% 6% 4 6% 9% 36%	4253
September	1st to 10th	Day	17% 8% 3 8% 4 4 5% 3 6% 8% 35%	2280
	11th to 20th	Day	16% 6% 3 5% 5% 4 4 4 6% 8% 40%	2214
	21st to end	Day	20% 9% 4 9% 5% 4 5% 4 5% 7% 29%	2022
October	1st to 10th	Day	22% 9% 2 8% 5% 4 4 3 5% 7% 31%	1900
	11th to 20th	Day	22% 15% 4 8% 4 4 4 2 3 5% 29%	1900
	21st to end	Day	25% 18% 4 8% 3 4 4 3 4 5% 22%	2090
November	1st to 10th	Day	14% 19% 4 7% 5% 5% 3 3 5% 6% 29%	1789
	11th to 20th	Day	14% 25% 6% 9% 4 3 4 4 4 6% 20%	1600
	21st to end	Day	18% 27% 7% 10% 4 3 4 2 5% 5% 15%	1600
December	1st to 10th	Day	16% 28% 14% 21% 3 2 3 2 2 2 7%	2600
	11th to 20th	Day	17% 21% 8% 17% 8% 5% 3 2 3 4 12%	2986
	21st to end	Day	18% 26% 8% 12% 8% 3 3 2 3 4 12%	3960
January	1st to 10th	Night	13% 25% 10% 20% 7% 4 3 2 3 3 9%	4569
	11th to 20th	Night	11% 21% 12% 20% 8% 6% 4 3 3 3 10%	4284
	21st to end	Night	20% 21% 10% 16% 10% 4 3 2 3 2 9%	4546
February	1st to 10th	Night	15% 20% 6% 16% 11% 5% 3 2 3 4 15%	2470
	11th to 20th	Night	11% 17% 9% 19% 9% 5% 5% 2 4 5% 14%	2403
	21st to end	Night	16% 17% 6% 17% 8% 4 4 2 4 3 19%	1951
March	1st to 10th	Night	19% 17% 5% 10% 5% 4 3 2 4 4 27%	3408
	11th to 20th	Night	17% 20% 9% 11% 5% 3 3 2 3 5% 22%	3479
	21st to end	Night	14% 14% 6% 12% 5% 4 3 3 4 5% 31%	3817
April	1st to 10th	Night	17% 17% 6% 8% 5% 4 4 3 4 5% 28%	1912
	11th to 20th	Night	19% 15% 3 6% 4 4 4 3 4 6% 34%	1875
	21st to end	Night	15% 14% 3 6% 5% 5% 4 4 6% 8% 30%	1743
May	1st to 10th	Night	24% 12% 3 7% 4 4 3 3 4 5% 30%	2833
	11th to 20th	Night	14% 12% 4 6% 5% 4 5% 4 5% 7% 33%	2537
	21st to end	Night	14% 8% 2 5% 3 3 4 3 6% 9% 42%	2738
June	1st to 10th	Night	14% 8% 3 8% 5% 4 6% 4 6% 8% 34%	1520
	11th to 20th	Night	13% 7% 3 6% 4 5% 5% 4 7% 8% 39%	1520
	21st to end	Night	14% 7% 3 7% 5% 5% 5% 2 6% 8% 39%	1520
July	1st to 10th	Night	13% 9% 2 7% 5% 4 4 4 5% 7% 40%	2520
	11th to 20th	Night	12% 8% 2 6% 4 4 5% 3 6% 8% 42%	2520
	21st to end	Night	12% 6% 3 6% 5% 4 5% 4 6% 8% 41%	3082
August	1st to 10th	Night	13% 10% 3 7% 4 4 5% 4 6% 8% 37%	2825
	11th to 20th	Night	17% 11% 3 7% 4 5% 5% 3 6% 7% 32%	2785
	21st to end	Night	9% 7% 2 7% 4 5% 5% 4 6% 8% 42%	3370
September	1st to 10th	Night	16% 8% 3 5% 3 4 3 4 5% 7% 42%	1900
	11th to 20th	Night	14% 7% 2 6% 4 4 4 2 5% 6% 46%	1962
	21st to end	Night	20% 8% 3 8% 5% 5% 4 4 5% 7% 31%	2157
October	1st to 10th	Night	19% 8% 3 7% 5% 4 4 3 5% 6% 36%	2280
	11th to 20th	Night	22% 11% 3 8% 5% 4 5% 3 4 6% 29%	2280
	21st to end	Night	27% 15% 3 6% 4 3 4 3 4 5% 25%	2508
November	1st to 10th	Night	16% 17% 4 8% 4 3 3 3 4 5% 32%	2506
	11th to 20th	Night	17% 22% 5% 9% 5% 4 4 4 4 5% 21%	2800
	21st to end	Night	16% 24% 7% 13% 5% 4 3 3 4 4 17%	2800
December	1st to 10th	Night	14% 25% 13% 19% 6% 4 3 2 3 3 8%	4580
	11th to 20th	Night	17% 22% 11% 16% 6% 4 3 2 2 3 12%	5208
	21st to end	Night	17% 23% 9% 15% 7% 4 3 3 3 4 11%	6996

Transparency (when cloud cover <= 30%)
Color Meanings: Too cloudy to forecast Poor Below Average Average Above average Transparent
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	78% 3 7% 8% 3	2598
	11th to 20th	Day	77% 3 6% 10% 4	2879
	21st to end	Day	82% 4 7% 5% 2	3133
February	1st to 10th	Day	76% 4 8% 8% 4	1710
	11th to 20th	Day	71% 4 6% 13% 5%	1672
	21st to end	Day	67% 4 9% 14% 5% 1	1500
March	1st to 10th	Day	59% 4 9% 23% 5%	3435
	11th to 20th	Day	59% 5% 15% 15% 5% 1	3480
	21st to end	Day	59% 4 8% 20% 8% 1	3815
April	1st to 10th	Day	58% 5% 10% 16% 11%	2267
	11th to 20th	Day	52% 6% 10% 19% 11% 1	2254
	21st to end	Day	54% 5% 10% 17% 13% 1	2454
May	1st to 10th	Day	54% 5% 9% 21% 9% 2	4120
	11th to 20th	Day	53% 10% 11% 18% 7% 1	4360
	21st to end	Day	40% 8% 13% 23% 14% 2	4837
June	1st to 10th	Day	48% 6% 12% 20% 13% 2	2660
	11th to 20th	Day	47% 7% 13% 21% 12%	2660
	21st to end	Day	45% 7% 13% 23% 12%	2660
July	1st to 10th	Day	43% 6% 13% 25% 13% 1	4370
	11th to 20th	Day	42% 7% 13% 22% 16%	4365
	21st to end	Day	44% 6% 13% 23% 13% 1	4324
August	1st to 10th	Day	49% 7% 13% 21% 11%	4091
	11th to 20th	Day	53% 7% 13% 21% 5%	4083
	21st to end	Day	42% 6% 11% 31% 10% 1	4253
September	1st to 10th	Day	47% 7% 10% 23% 12% 1	2280
	11th to 20th	Day	41% 6% 12% 25% 15% 1	2214
	21st to end	Day	53% 7% 10% 20% 10% 1	2022
October	1st to 10th	Day	47% 5% 12% 22% 14% 1	3160
	11th to 20th	Day	51% 3 14% 15% 14% 4	3140
	21st to end	Day	52% 3 15% 22% 8% 1	3428
November	1st to 10th	Day	55% 5% 11% 16% 10% 2	1789
	11th to 20th	Day	64% 5% 10% 13% 6% 2	1600
	21st to end	Day	72% 4 10% 10% 4 1	1600
December	1st to 10th	Day	86% 2 5% 6% 1	2600
	11th to 20th	Day	78% 4 7% 9% 2	2986
	21st to end	Day	77% 3 9% 7% 3	3960
January	1st to 10th	Night	80% 3 8% 6% 2	4569
	11th to 20th	Night	79% 4 8% 7% 2	4284
	21st to end	Night	82% 3 5% 7% 2	4546
February	1st to 10th	Night	74% 4 9% 10% 4	2470
	11th to 20th	Night	73% 5% 7% 11% 4	2405
	21st to end	Night	69% 4 8% 12% 7% 1	1951
March	1st to 10th	Night	61% 5% 8% 21% 4	3418
	11th to 20th	Night	64% 4 10% 16% 5%	3480
	21st to end	Night	54% 5% 9% 18% 12% 2	3817
April	1st to 10th	Night	59% 5% 10% 16% 10%	1912
	11th to 20th	Night	52% 6% 11% 17% 13% 2	1875
	21st to end	Night	51% 6% 10% 19% 11% 2	1743
May	1st to 10th	Night	54% 6% 9% 19% 9% 2	2840
	11th to 20th	Night	49% 10% 13% 21% 7% 1	2538
	21st to end	Night	37% 8% 12% 24% 14% 5%	2739
June	1st to 10th	Night	45% 7% 12% 23% 13% 1	1520
	11th to 20th	Night	40% 8% 13% 24% 13% 2	1520
	21st to end	Night	42% 7% 12% 27% 11% 1	1520
July	1st to 10th	Night	43% 5% 13% 22% 15% 2	2480
	11th to 20th	Night	39% 5% 16% 26% 13% 1	2472
	21st to end	Night	40% 6% 15% 23% 16% 1	2984
August	1st to 10th	Night	45% 7% 13% 27% 8% 1	2814
	11th to 20th	Night	49% 6% 16% 22% 7%	2812
	21st to end	Night	37% 6% 14% 32% 9% 1	3370
September	1st to 10th	Night	40% 7% 13% 25% 13% 2	1900
	11th to 20th	Night	38% 6% 13% 25% 17% 1	1962
	21st to end	Night	51% 7% 12% 18% 11% 1	2157
October	1st to 10th	Night	49% 4 8% 21% 18%	3800
	11th to 20th	Night	50% 4 11% 16% 15% 4	3779
	21st to end	Night	46% 4 15% 24% 10% 1	4120
November	1st to 10th	Night	51% 6% 11% 20% 10% 2	2506
	11th to 20th	Night	63% 5% 10% 13% 6% 3	2800
	21st to end	Night	70% 5% 10% 12% 3	2800
December	1st to 10th	Night	83% 3 7% 6% 1	4580
	11th to 20th	Night	78% 3 7% 10% 3	5208
	21st to end	Night	78% 4 7% 8% 3	6996

Seeing (when cloud cover <= 80%)
Color Meanings: Too cloudy to forecast Bad 1/5 Poor 2/5 Average 3/5 Good 4/5 Excellent 5/5
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	31% 31% 27% 10% 3 1	200
	11th to 20th	Day	37% 32% 23% 5% 2	287
	21st to end	Day	30% 31% 27% 10% 2	300
February	1st to 10th	Day	39% 26% 30% 5% 1	270
	11th to 20th	Day	34% 33% 29% 3 1	270
	21st to end	Day	43% 24% 26% 5% 1	300
March	1st to 10th	Day	34% 23% 28% 13% 3	460
	11th to 20th	Day	31% 26% 30% 10% 2 1	460
	21st to end	Day	37% 22% 24% 13% 4 1	506
April	1st to 10th	Day	32% 24% 25% 14% 5% 1	460
	11th to 20th	Day	34% 23% 23% 11% 7% 2	452
	21st to end	Day	29% 19% 32% 15% 4 1	460
May	1st to 10th	Day	33% 20% 25% 15% 6% 2	463
	11th to 20th	Day	26% 15% 28% 21% 9% 1	487
	21st to end	Day	16% 15% 30% 21% 13% 5%	529
June	1st to 10th	Day	22% 18% 30% 20% 9% 2	490
	11th to 20th	Day	20% 12% 28% 24% 14% 2	490
	21st to end	Day	19% 14% 36% 22% 8% 1	490
July	1st to 10th	Day	12% 10% 31% 24% 17% 6%	485
	11th to 20th	Day	14% 10% 28% 27% 16% 5%	484
	21st to end	Day	13% 9% 37% 24% 13% 4	532
August	1st to 10th	Day	13% 9% 29% 26% 15% 8%	486
	11th to 20th	Day	17% 9% 28% 24% 14% 8%	479
	21st to end	Day	17% 10% 27% 24% 14% 8%	539
September	1st to 10th	Day	20% 11% 23% 22% 16% 7%	490
	11th to 20th	Day	15% 8% 23% 22% 23% 9%	490
	21st to end	Day	24% 15% 26% 17% 13% 4	490
October	1st to 10th	Day	24% 13% 26% 18% 13% 4	490
	11th to 20th	Day	30% 20% 27% 14% 7% 2	490
	21st to end	Day	38% 16% 28% 16% 2	539
November	1st to 10th	Day	30% 19% 27% 16% 5% 2	385
	11th to 20th	Day	40% 21% 28% 9% 2 1	200
	21st to end	Day	38% 23% 32% 7% 1	200
December	1st to 10th	Day	43% 23% 25% 5% 4 1	200
	11th to 20th	Day	42% 24% 28% 6% 1	200
	21st to end	Day	39% 23% 33% 3 2	220
January	1st to 10th	Night	31% 29% 26% 11% 3	800
	11th to 20th	Night	31% 27% 28% 13% 2	800
	21st to end	Night	25% 29% 30% 14% 2	841
February	1st to 10th	Night	30% 26% 29% 15% 1	760
	11th to 20th	Night	29% 28% 32% 11% 1	743
	21st to end	Night	32% 25% 29% 12% 2	628
March	1st to 10th	Night	28% 21% 34% 14% 3	760
	11th to 20th	Night	34% 20% 24% 17% 4 1	760
	21st to end	Night	25% 20% 33% 15% 6% 1	836
April	1st to 10th	Night	28% 19% 30% 20% 3	760
	11th to 20th	Night	30% 17% 27% 19% 7% 1	751
	21st to end	Night	22% 13% 31% 28% 6%	603
May	1st to 10th	Night	22% 12% 24% 29% 12%	570
	11th to 20th	Night	16% 11% 29% 35% 8%	403
	21st to end	Night	16% 9% 24% 32% 17% 2	411
June	1st to 10th	Night	16% 6% 27% 36% 13% 1	380
	11th to 20th	Night	18% 9% 23% 38% 12%	380
	21st to end	Night	16% 6% 31% 33% 14%	380
July	1st to 10th	Night	12% 6% 17% 45% 16% 4	370
	11th to 20th	Night	11% 3 24% 38% 23% 1	368
	21st to end	Night	15% 4 21% 36% 24% 1	619
August	1st to 10th	Night	13% 4 20% 35% 27% 2	567
	11th to 20th	Night	15% 5% 18% 30% 29% 2	564
	21st to end	Night	12% 6% 22% 34% 22% 2	769
September	1st to 10th	Night	19% 8% 21% 30% 20% 2	760
	11th to 20th	Night	15% 8% 18% 27% 28% 4	760
	21st to end	Night	23% 11% 21% 26% 16% 3	760
October	1st to 10th	Night	24% 11% 25% 23% 16% 2	760
	11th to 20th	Night	29% 14% 28% 22% 6% 1	760
	21st to end	Night	34% 15% 28% 19% 4	836
November	1st to 10th	Night	27% 15% 28% 23% 7%	780
	11th to 20th	Night	32% 19% 27% 16% 5% 1	800
	21st to end	Night	31% 24% 28% 14% 4	800
December	1st to 10th	Night	36% 25% 26% 11% 3	800
	11th to 20th	Night	34% 25% 27% 12% 2	800
	21st to end	Night	33% 24% 30% 12% 1	880

Page generated at 2025-01-19 03:06:43. Version ac07

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